Conventionally, for belt layers of a pneumatic radial tire, a wide strip member in which a number of aligned reinforcement cords are embedded in an unvulcanized rubber is cut obliquely at a predetermined angle to a belt width, rectangular strip pieces which have been cut obliquely are joined together in such a manner that cut sides thereof constitute both left and right edge portions so as to form a long belt member, and the long belt member is coiled into a roll so as to be stocked temporarily.
This belt member is uncoiled from the roll when molding a belt layer for a tire and is cut along the direction in which the reinforcement cords are aligned to a length which corresponds to a circumferential length of a belt layer, so as to obtain a belt member of a predetermined length.
However, in belt members for one tire, since a width and length thereof differ according to tire sizes and a cord angle thereof differs according to tire specifications, belt members molded in the way described above need to be stocked as belt materials which differ in dimension according to specifications. Consequently, since an extremely large number of types of belt members are prepared as intermediate members, wide stock spaces and intermediate stocks need to be possessed, and it has been difficult to cope with a production of a wide variety of types of products in small lot sizes.
Then, in producing a belt member by joining together a plurality of strip pieces obtained by cutting a strip member of a constant width to a regular size in such a state that non-cut surfaces of the strip pieces so cut are brought into abutment with each other, a method is disclosed for producing a belt member of a desired width and length by adjusting the length of strip pieces to be obtained by cutting in such a manner that the number of strip pieces to be joined together becomes an integer and adjusting a cutting angle of the strip pieces (for example, Patent Document 1).
In the producing method, however, there is caused a problem that in order to obtain a belt member of a desired width and length, the cutting angle of the strip pieces which corresponds to the cord angle needs to be adjusted and a desired cutting angle which is determined from a tire performance required has to be changed.
[Patent Document 1] JP-A-11-99564